Electric switch



Aug. 30, 1932. M PERSONS 1,874,116

ELECTRIC SWITCH Filed Oct. 9. 1929 2 Sheets-Sheet l IIIIIII Aug. 30, 1932. PERSONS 1,874,116

ELECTRIC SWITCH Filed Oct. 9, 1929 2 Sheets-Sheet 2 Patented Aug. 30, 1932 PATENT OFFICE LAURENCE M. PERSONS, OF ST. LOUIS, MISSOURI ELECTRIC SWITCH Application filed October 9, 1929. Serial No. 398,538.

This invention relates to electric switches and is illustrated, by way of example, as being applied to a temperature regulating thermostat arranged to make and break an electrical circuit when the temperature to which the thermostat is subjected passes beyond predetermined limits.

One object of the invention is to provide an electric switch in which the contacts will be brought together or separated by a quick motion.

Another object of the invention is to provide an electric switch of improved construction and operation.

Another object of the invention is to provide a thermostat of simple and economical construction which will produce a quick break of the electric circuit to avoid arcing.

A further object of the invention is to provide a thermostat which will operate between narrow limits.

Still another object of the invention is to provide a switch of the class described in which a wiping action will be setup between the contacts thereof when the same are opened and closed, thus keeping the surface of the contacts clean at all times.

Other objects and advantages will appear from the following description.

The invention is exemplified in the combination and arrangement of parts shown in the accompanying drawings and described in the following specification, and it is more M particularly pointed out in the appended claims.

In the drawings- Figure 1 is a front elevation of athermostat embodying the present invention, with 19 the cover in place;

Figure 2 is a view similar to Figure 1, with the cover removed;

Figure 3 is a vertical section on line 33 of Figure 2; Figure 4 is a horizontal section on line 4-4 of Figure 2;

Figure 5 is a horizontal section on line 5-5 of Figure 2;

Figure 6 is a view, similar to Figure 2, showing a modified form of the invention;

Figure 7 is a section on line 7-7 of Figure 6;

Figure 8 is a section on line 88 of Figure 6;

Figure 9 is a perspective view of a portion of the control magnet having a make and break contact thereon; and

Figure 10 is a perspective view of the contact member arranged to contact with that shown in Figure 9.

The form of the invention illustrated in the drawings, b way of example, is especially designed or controlling the temperature of brooders for small chickens, but it will be understood that the invention is not confined to use with any particular form of device, the temperature of which is to be .controlled.

In the form of the invention shown in Figures 1 and 5 inclusive, a sheet metal base 10 is provided which may be attached to the side wall of a brooder or otherwise supported in a position where it is subjected to the temperature to be controlled. A supporting plate 11 has a permanent bar magnet 12 mounted thereon and secured by straps 13 and screws 14. The screws 14 pass through the plate 11 and the base 10 and are provided with nuts 15 for holding the parts together. At one side of the plate 11 is anoutwardly bent arm 16 30 to which a U-shaped strip of thermal metal 17 is attached by screws 18. The metal 17 may be composed of an inner strip of copper and an outer strip of invar steel, or any other bi-metal arrangement which will cause a 86 tendency of the legs of the U to spread on increase in temperature. By arranging the metal in a U shape, not only is an economy of space efi'ected, but an increased movement for temperature changes is also secured. The free leg of the strip 17 is provided with a resilient continuation 19 having a spring 20 secured to the end thereof and provided with an adjustment screw 21. A contact point 22 is mounted on the spring 20 in position to co-operate with a contact point 23 formed on the end of a screw 24. The spring 20 for the contact 22 helps to prevent accidental engagement and disengagement of the points 22 and 23 which. might otherwise result from vibration of the support on which the thermostat is carried. The spring 19 when bending to open or close the contacts 22 and 23, causes the upper contact to wipe across the lower contact which keeps the contacts perfectly clean and prevents them from becoming pitted. The screw 24 is threaded through a block 25, the block forming the head of a screw 26 which extends through the plate 11, but is insulated therefrom. The screw 26 is provided with a nut 27 for holding it in place.

A plate 28 is clamped between the block and the insulation for the screw 26 and carries a binding post 29 for the attachment of an electric conductor. binding post 30 is also mounted on the plate 11. The binding posts 29 and 30 are attached to the conductors of an electric circuit for controlling any form of heat element. The thermostat may be placed in series, for instance, with the heating element for a brooder so that the heating current will pass through the contacts 22 and 23. Where a heavy heatlng current is required, the thermostat may be connected in a control circuit and not directly in' the heating circuit itself.

The arm 16 is provided with an extension 31 having a screw 32 threaded therethrough and bearing against the inner face of the thermal metal 17 near its supporting screws 18. By

forcing the screw 32 against the surface of the strip 17, the contact point 22 will be swung away from the point 23 and by loosening the pressure of the screw 32 upon the strip 17, the contact point 22 will be permitted to move inwardly toward the point 23. In this way the temperature at which the contact point 22 will leave the point 23, is regulated. The screw 32 is provided with an arm 33 which projects upwardly through a. slot 34 in the cover 35. The arm 33 is arranged to move adjacent a scale 36 formed on the cover and the scale is graduated to indicate the temperature maintained by the thermostat. When the temperature exceeds that indicated by the arm 33, the contacts 22 and 23 will be separated and when the temperature falls below the indicated temperature, the contacts will be brought together. Of course, a slight variation at either side of the indicated temperature may be required to produce movement of the con act points. This difi'erence between the m ke and break temperatures serves to prevent too frequent closing and opening of the circuit which would otherwise occur if the make and break temperatures were the same or approximately the same,

especially if the instrument were mounted where it would be subject to jarring.

The arm 19 carriesa screw 37 having its head 38 disposed adjacent the end of the permanent magnet 12; The screw 38 is adjusted so that when the points 22 and 23 are in contact, the head of the screw will just clear the surface of the magnet 12. As the tememme perature increases, the attraction of the magnet for the screw 38 will hold the screw from movement until a certain resilient force is exerted by the strip 18 and arm 19. When this force becomes sufliicient to overcome the attraction of the magnet for the screw, the contact 22 will be moved out with a quick action for as soon as the screw 28 begins to move away from the magnet, the force of the magnet rapidly decreases so that when the parts are once released the contacts will spring apart with a sudden movement, thus avoidlng arcing at the contact points. This quick'action is augmented by the fact that the force exerted by the magnet on its armature is inversely proportional to the square of the distance of the armature from the magnet while the force exerted by the spring is directly proportional only to the first power of the deflection of the spring. As the armature moves away from the magnet, therefore, the force exerted by the magnet decreases much more rapidly than that exerted by the spring so that when movement is once started the accelerating force on the armature increases and a quick break is secured. A quick contact is also efi'ected for the reason that as the screw 38 moves inwardly under the action of the metal strip 17 it will approach the magnet 12 until the magnetic attraction overcomes the resiliency of the support for the screw. As the screw begins to move inwardly under the influence of the magnetic field, the force of the magnetic field rapidly increases so that a quick make as well as a quick break in the circuit is effected.

In the form of the invention shown in Figures 6 to 10, inclusive, 9. base block 39 of dielectric material is provided. An angle bracket 40 is mounted on the block 39 and carries the thermal strip 17 and associated parts. ever, the magnet 12 is rovided with a binding post 41 so that t e magnet forms one terminal'for the electric circuit. A portion of the end of the magnetis provided with a coating 42 of silver or other suitable contact metal and the head of the screw 38 is also coated with similar metal 43. The coatings 42 and 43 are of non-magnetic metal so that the parts will not adhere when brought. together. The magnet 12 is insulated from the metal strip 17 by the base block 39. This form of the invention operates in a manner similar to that already described, except that contact is made directly with the permanent magnet 12, which thus serves the double purpose of quick make and break, and also supports the contact point for the electricalcircuit. v

' In the form of the invention shown in Figures 6 to 10, inclusive, the close proximity of the magnet to any spark produced by separating the contacts permits the magnet to In this form of the invention, howoperate as a magnetic blow-out for extin contact carried b guishing the spark. This characteristic is of great advantage in many instances, because it prevents damage to the contact points and also reduces the fire hazard.

It will be observed, as from Figure 2, that the circuit controlled by the thermostat extends through the binding post 29 and 30 and includes the member 17, its extension 19 and the opposed contacts 22 and 23. One effect of the passage of current through the member 17 is to cause a slight flexure in one direction when the circuit is closed, and a corresponding slight flexure in the op osite direction when the circuit is broken, dire to the heat caused by resistance to the passage" of current through the member 17. This inclusion of the bimetallic strip or temperature responsive member 17 in the circuit reduces the lag which otherwise exists to a considerable degree in the use of a thermostat of this type. This resistance heating effect, espeeially when combined with magnetic snap action, results in an extremely sensitive thermostat which makes or breaks at a temperature very close to the temperature at which it is set.

I claim:

.1. In a temperature responsive switch, a base, a substantially U-shaped thermostatic element having one leg thereof fixedly secured to the base, said other leg of the thermostatic element being free and provided with an arm extending therefrom in general alinement therewith, an armature carried by the arm and extending inwardly therefrom, a contact carried by the arm beyond the armature, a permanent bar magnet carried by the base and positioned between the legs of the thermostatic element and extending into operative relation with the armature, a second the base and operatively associated with t e first mentioned contact, and adjusting means carried by the base and engaging the fixed leg of the thermostatic element adjacent to its point of securement to the base and operating to flex said leg to a greater or lesserextent whereby to vary the point of engagement of said contacts.

2. In a temperature responsive switch, a base, a substantially U-shaped thermostatic element having one leg thereof fixedly secured to the base, said other leg of the thermostatic element being free and provided with an arm extending therefrom in general alinement therewith, an armature carried by the arm and extending inwardly therefrom, a contact carried by the arm beyond the armature, a permanent bar magnet carried by the base and positioned between the legs of the thermostatic element and extending into operative relation with the armature, a second contact carried by the base and operatively associated with the first mentioned contact, adjusting means carried by the base and engaging the fixed leg of the thermostatic element adjacent to its point of securement to the base and operating to flex said leg to a greater or lesser extent whereby to vary the point of engagement of said contacts, said last mentioned means including an arm carried by the base and extending within, and generally parallel to the fixed leg of the thermostatic element, and a set screw carried by said arm and engageable with said leg beyond the point of securement thereof to the base.

3. In a temperature responsive switch, a base, a substantially U-shaped thermostatic element having one leg thereof fixedly secured to the base, said other leg of the thermostatic element being free and provided with an arm extending therefrom in general alinement therewith, an armature carried by the arm and extending inwardly therefrom, a contact carried by the arm beyond the armature, a permanent bar magnet carried by the base and positioned between the legs of the thermostatic element and extending into operative relation with the armature, a second contact carried b the base and operatively associated with't e first mentioned contact,

and adjusting means carried by the base and engaging the fixed leg of the thermostatic. element adjacent to its point of securement to the base and operating to flex said leg to a greater or lesser extent whereby to vary the point of engagement of said contacts, said armature being adjustably mounted on the arm whereby to provide a clearance between it and said permanent magnet when said contacts are engaged.

4. In a temperature responsive switch, a

base, a substantially U-shaped thermostatic element having one leg thereof fixedly secured to the base, said other leg of the thermostatic element being free and provided with an arm extending therefrom in general alinement therewith, an armature carried by the arm and extending inwardly therefrom, a contact carried by the arm beyond the armature, a permanent bar magnet carried by the base and positioned between the legs of the thermostatic element and extending into operative relation with the armature, a second contact carried by the base and operatively associated with the first-mentioned contact.

and adjusting means carried. by the base and engaging the fixed leg of the thermostatic element adjacent to its point of securement to the base and operating to flex said leg to a greater or-lesser extent whereby to vary the point of engagement of said contacts, that portion of the armwhich carries the first mentioned contact being resilient whereby to provide a wiping action between said contacts as the same are made and broken due to the flexure of said resilient portion.

Signed at St. Louis and State of Missouri, this 4th day of October 1929. LAURENCE M. PERSONS. 

